Various apparatus have long been employed for intravenous infusion of fluids into a patient at a controlled rate and over extended periods of time, the most common of these being simply a gravity flow technique wherein a container of the desired medicament, drug, or the like is suspended above the patient and infusion is effected by gravity flow of the fluid from a container suspended above the patient through a tube and into the patient. However, rather than relying simply on gravity flow, various apparatus and techniques were devised for better controlling the rate of infusion as, for example, depicted in U.S. Pat. No. 4,132,231 to Puccio and U.S. Pat. No. 4,381,006 to Genese. Such devices relied upon a system of weights or coil springs employed to activate the plunger of a conventional syringe in a controlled manner as a function of the weight or spring tension.
Such approaches suffered from serious drawbacks, not the least of which was the lack of portability, simplicity, and low cost of such devices which has become more important recently with the advent of increased frequency in ambulatory patient care. Accordingly, yet additional devices were developed to meet this need such as a spring-loaded cylindrical carrier of a conventional syringe depicted in U.S. Pat. No. 3,880,163 to Ritterscamp and like devices. Such devices still suffered from obvious drawbacks relating to the number of moving parts required, undue weight and bulk, unreliability and inflexibility of infusion rates due to difficulty in controlling and varying spring tension over time and related mechanical complexity problems, and the like, giving rise to the need for a simpler drug dispensing device. Recently, such a device has been developed as depicted in U.S. Pat. No. 4,201,207 to Buckles, et al. In such apparatus, an elastomeric reservoir in the form of a bladder is provided which is distended upon filling of the bladder with the drug to be administered. In some forms, the bladder apparatus is provided in the form of a cylindrical balloon disposed within a rigid housing. The energy stored in the resilient walls of the distended elastomer provides the force required to infuse the drug contained within the bladder through an appropriate tube and into the patient.
Unfortunately, while solving at least the problem of portability, such devices have suffered from numerous other drawbacks. First, there have been problems in such continuous infusion devices with establishing a constancy of delivery rate of the drug thought to be caused by a loss of pressure provided by the bladder for a constant volume with time. Moreover, it has been found that excessive retention of drugs within the bladder occurs after a complete retraction of the elastomer, i.e., it is difficult to completely evacuate the bladder during the infusion process. This in turn has been found extremely undesirable inasmuch as some of the drugs which are administered are extremely expensive and it has been found that loss rates by volume ranging from 5-25% of the drug have been experienced. It has oftentimes also been found difficult to prime such apparatus and to manually control the infusion rate if desired. Problems have also been experienced with the bladder breaking or leaking which can at times be extremely serious not only due to the wastage of drugs and dangerous conditions which may arise if the required dosage is not thus administered, but additionally due to the deleterious effect of some of the drugs when they are contacted by those for whom they are not intended. For example, it has long been known that cancer treatment drugs are themselves carcinogenic to various degrees and it is thus highly undesirable for hospital pharmacists, nurses and other personnel administering the drugs to come into contact with them on a frequent and recurring basis. However, the possibilities of this happening have been found to be undesirably great with respect to bladder-type infusion devices due to the aforementioned breakage, leakage, and the like.
Still other problems are also associated with the bladder-type infusion devices as well as other types of devices employing, for example, motors and batteries to effect the pumping of the drug through the tube. Many of these devices are difficult to adjust in terms of flow rate, particularly with respect to the bladder-type devices. Regarding the electronic devices employing motors, instrumentation, and the like, they obviously suffer from the drawback of being more complicated, costly, requiring recharging of batteries if in a portable version, as well as difficulty in instructing the patient in proper use. Whereas the bladder-type devices are certainly more disposable than other apparatus for infusing drugs, difficulty has further been experienced in sporadic flow rates thought to be caused by varying pressures exerted by the bladder on the drug, such pressures being dependent upon the volume of the drug contained within the bladder reservoir and also being temperature dependent.
Thus, a portable continuous infusion device was highly desired which would be both of a simple construction, easy to use, portable, concealable, and of a low cost so as to render it partially disposable while at the same time providing portions which are re-usable. Moreover, such a device was further highly sought after which required no maintenance, provided for a completely sealed drug in the event of syringe tip breaks and cracks and the like so as to avoid contamination, mess, and the aforementioned problems associated with medical personnel coming in contact with the drugs. Such an infusion device was also sought which employed a conventional syringe for ease of charging the device with the desired drug inasmuch as pharmacists, nurses, and the like may in a typical day have to prepare as many as 50 or 60 such devices for use by patients. Still further, improvements were sought in the ability of the device to be easily adjusted in terms of flow rate so as to contribute to a more predictable flow rate. It was further desired to avoid the aforementioned problems associated with wastage of the drug due to the bladder's inability to entirely evacuate the drug. These and other deficiencies of the prior infusion devices are overcome by the present invention and a novel portable continuous infusion device is provided achieving all of the hereinbefore noted and sought after characteristics as well as other.